Power devices are utilized in a plurality of circuit applications that require high voltage and current capability, for example, automotive circuits. However, power devices must be protected from large surge currents which could destroy the device.
Control circuits are typically utilized to protect power transistors by, for example, monitoring the current flowing through the power transistor. Some control circuits have an input driven by a voltage signal. However, this type of circuit is not suitable for use as a high side switch wherein the load is connected to the emitter of a power transistor. Also, voltage control driven circuits are limited by ground bounce, especially when driving large inductive loads. Moreover, these applications require a current input control circuit.
One such control circuit for protecting a power device is fully disclosed in U.S. Pat. No. 5,285,346 issued to Davies et al. on Feb. 8, 1994 and entitled "CURRENT DRIVEN CONTROL CIRCUIT FOR A POWER DEVICE". The control circuit disclosed here is a current driven control circuit. However, this current driven control circuit requires the input current to be limited in a controlled manner, for example by a staircase input signal.
Hence, there is a need for an improved current controlled circuit for protecting a power transistor that monitors the condition of the power transistor and does not require a specialized input current signal.